The invention is based on a brake valve as generally defined herein. A brake valve connected to a pressure supply apparatus and a return flow container and used for feeding brake pressures into a brake system is known from U.S. Pat. No. 4,463,561. As its valve elements, this brake valve has two balls and two ball seats. The first ball is secured to a control rod and is normally spaced apart from its ball seat; the second ball is moved toward its ball seat by a closing spring, and when it is seated it is additionally pressed against the ball seat by the pressure of the pressure supply apparatus. To feed brake pressure into the brake system, the first ball is pressed against its ball seat, and the second ball is raised from its ball seat by means of a tappet, counter to the force of the spring and counter to the pressure of the pressure supply apparatus. A brake valve of this type is reliably tight, so that during pauses in brake valve operation the pressure supply system does not need to perform any pumping work to compensate for leakage. However, because of the diameter of the ball seat, through which increases in brake pressure are effected, the forces required for raising the ball from its ball seat are disadvantageously great. The magnitude of these forces fluctuates in accordance with the level of pressure furnished by the pressure supply apparatus. A further disadvantage is that to prevent leakage of pressure medium along the displaceable control rod, two seals are required, which must be capable of withstanding the maximum possible pressure provided by the pressure supply apparatus and accordingly are a source of frictional resistance. This frictional resistance is also a hindrance to fine control of brake pressures.